This application incorporates by reference Taiwan application Serial No. 090131394, filed Dec. 18, 2001.
1. Field of the Invention
The invention relates in general to the liquid crystal display (LCD) with slant structures, and more particular to the liquid crystal on Silicon (LCoS) with slant structures.
2. Description of the Related Art
LCoS with higher resolution is now highly demanded and becomes more popular because first, the markets of portable equipments, such as Personal Digital Assistance (PDA) and mobile phones, and the large size monitor, such as project television, are growing rapidly and also the higher image quality is demanded. The structure of the LCoS is different from the conventional LCD by using one silicon substrate and one glass substrate as its two opposite substrates. And liquid crystal molecules are then sandwiched between the two substrates.
In FIG. 1, the cross section of a single pixel 100 of a reflective LCoS is shown. The reflective LCoS has an upper plate 101 and a lower plate 102. The lower plate 102 comprises a silicon substrate 104. By using the semiconductor manufacturing process, devices such as the control circuit (not shown) of the pixel, the pixel electrode 105, the reflector 106 and so on are fabricated on the silicon substrate 104. The upper plate 101 of the LCoS comprises a glass substrate 107 and a transparent electrode 108 on the glass substrate 107 The upper plate 101 and the lower plate 102 are opposite to each other and there is a gap in-between. The liquid crystal molecules are filled in the gap to form a liquid crystal layer 109. Moreover, an alignment film 110 is formed over the upper plate 101 and another alignment film 112 is formed over the lower plate 102. The alignment films 110 and 112 control the orientation of the liquid crystal molecules. That is to say the liquid crystal molecules of the liquid crystal layer 109 orientate along the indication direction of the alignment films 110 and 112. On the LCoS panel, all the pixel electrodes 105 are not connected to each other and separated by slits 114. The slit 114 are either covered by alignment film 112 or filled with an insulating material.
Conventionally, the indication direction of alignment films is formed by rubbing. The rubbing process is performed by using special velvet cloth to rub the alignment film in a certain direction so that the alignment films 110 and 112 can have indication direction. However, it is difficult to always precisely match the special velvet cloth and the alignment film. The deviation of the special velvet cloth during the rubbing process can cause the unevenness of the alignment films. Also, electrostatic discharge generated during the rubbing process can influence the operation of the electric devices and the orientation of the liquid crystal molecules. Furthermore, the remaining residues can scratch the alignment films 110 and 112.
In addition to rubbing process, other methods such as photo-align is also available. However, it is not mature enough to be applied in large-scale.
Moreover, while a voltage is applied to the transparent electrode 108 of the upper plate 101 and the pixel electrode 105 of the lower plate 102, the orientation of the liquid crystal molecules in the liquid crystal layer 109 will change and consequently the light transmissivity of the liquid crystal molecules will also change. In other words, the orientation of the liquid crystal molecules in the pixels and the brightness of the pixels can be controlled by the applied voltage. However, to show a complete image, the brightness and the applied voltage of each pixel are not equal. A transverse electric field exists at two the edge of every two adjacent pixels with unequal applied voltage. The strength of the transverse electric field and the difference of the applied voltage of two adjacent pixels are in direct proportion. As a result of the transverse electric field, the brightness of the edge of pixels may deviate from expectation and even dark bands may exist on the image. This is so-called fringe effect. Therefore, it is a hot issue to eliminate the fringe effect in order to produce better image.
It is therefore an object of the invention to provide an LCD with slant structures with the following advantages:
1. using an alternative process without the drawbacks of rubbing; and
2. having reduced transverse electric field and no fringe effect.
The invention achieves the above-identified objects by providing an LCD including a first plate, a second plate opposite to the first plate and a liquid crystal layer between the first plate and the second plate. The first plate further includes a first alignment film over the first plate and the first alignment film has an indication direction. The second plate includes a number of pixels. Each of the pixels includes the following from the bottom to the top: a pixel electrode, a reflector, a thin film layer consisting of a number of thin films, and a second alignment film. The thin films are formed by photolithography and the thin film layer and the second alignment film together form one slant structure with a single inclined side.